that effect can be easily seen today in a living city, a city like fez, morocco. archaeologists have come to fez because the same high degree of specialization suggested by the ruins of ostia can be seen here in the flesh. the population and density of the old city of fez has remained the same since the 10th century. archaeologist david webster. the old city of fez had about 120,000 people for its total population. this would have been an equivalent of a population density of tens of thousands of people per square mile. now, the only reason why that was possible, especially in a nonindustrial context, was that you had a very effective agricultural environment around fez within, say, 15 or 20 miles radius. but you also had very effective forms of nonhuman transport -- donkeys, camels, horses, mules -- that could bring in all of the kinds of supplies that the city needed. now, that's one reason why you had such high population densities. one of the effects of really high population densities, of course, is to create very dense urban markets, lots of consumers concen